By the operation of meteoric agencies, iron pyrites readily pass into limonite often with retention of external form; and the masses of "gozzan" or "gossan" on the outcrop of certain mineral-veins consist of rusty iron ore formed in this way, and associated with cellular quartz.

Many deposits of limonite have been found, on being worked, to pass downwards into ferrous carbonate; and crystals of chalybite converted superficially into limonite are well known.

Minerals, like glauconite, which contain ferrous silicate, may in like manner yield limonite, on weathering.

Granular and concretionary limonite accumulates by organic action on the floor of certain lakes in Sweden, forming the curious "lake ore."

Limonite often forms a cementing medium in ferruginous sands and gravels, forming "pan"; and in like manner it is the agglutinating agent in many conglomerates, like the South African "banket," where it is auriferous.

In iron-shot sands the limonite may form hollow concretions, known in some cases as "boxes."

Bog iron ore is an impure limonite, usually formed by the influence of micro-organisms, and containing silica, phosphoric acid and organic matter, sometimes with manganese.

The various kinds of brown and yellow ochre are mixtures of limonite with clay and other impurities; whilst in umber much manganese oxide is present.

C. Ullmann's name of stilpnosiderite, from the Greek ariAirvOs (shining) is sometimes applied to such kinds of limonite as have a pitchy lustre.

Deposits of limonite in cavities may have a rounded surface or even a stalactitic form, and may present a brilliant lustre, of blackish colour, forming what is called in Germany Glaskopf (glass head).

It often happens that analyses of brown iron ores reveal a larger proportion of water than required by the typical formula of limonite, and hence new species have been recognized.

On the other hand there are certain forms of ferric hydrate containing less water than limonite and approaching to haematite in their red colour and streak: such is the mineral which was called hydrohaematite by A.

It probably represents the partial dehydration of limonite, and by further loss of water may pass into haematite or red iron ore.

On exposure to meteoric influences pyrites commonly becomes brown, by formation of ferric hydrate or limonite, whence the change is called "limonitization."

They are four important iron ores, magnetite, haematite, limonite and siderite, and one of less but still considerable importance, pyrite or pyrites.

Limonite, 2Fe20 3, 3H 2 0, contains 59.9% of iron.

Under all these three conditions the diamond is associated with fragments of the rocks of the country and the minerals derived from them, 'especially quartz, hornstone, jasper, the polymorphous oxide of titanium (rutile, anatase and brookite), oxides and hydrates of iron (magnetite, ilmenite, haematite, limonite), oxide of tin, iron pyrites, tourmaline, garnet, xenotime, monazite, kyanite, diaspore, sphene, topaz, and several phosphates, and also gold.

Sandstone of various colours was the chief material employed by the Khmers; limonite was also used.

Iron is widely diffused, principally in the form of magnetite, brown haematite, limonite and bog iron.

Ferric oxide or iron sesquioxide, Fe203, constitutes the valuable ores red haematite and specular iron; the minerals brown haematite or limonite, and gothite and also iron rust are hydrated forms. It is obtained as a steel-grey crystalline powder by igniting the oxide or any ferric salt containing a volatile acid.

Their typical colour is blackishblue, owing to the abundance of sulphuretted hydrogen; when fresh they have a sulphurous odour, when weathered they are brown, as their iron is present as hydrous oxides (limonite, &c.).

When limonite is dehydrated and deoxidized in the presence of carbonic acid, it may give rise to chalybite.

Goethite, limonite and haematite are found in New South Wales, at the junction of the Hawkesbury sandstone formation and the Wianamatta shale, near Nattai, and are enhanced in their value by their proximity to coal-beds.